Calibrating the element composition of Donax deltoides shells as a palaeo-salinity proxy

Bivalve shell chemistries provide valuable insights into past environments if relationships between shell chemistry and environmental conditions are known. This study assessed the suitability of Goolwa cockle (Donax deltoides) shell element composition as an environmental proxy for southern Australia, a region lacking high-resolution environmental records. Cockles were collected along an environmental gradient and the element composition of corresponding water and shell samples were quantified using a combination of ICP-AES and ICP-MS (for water samples), and LA-ICP-MS (for shells). Of the elements analysed, Ba/Ca, Li/Ca and Mg/Ca in shells reflected ambient water chemistries. Shell Ba/Ca concentrations showed a significant, negative relationship with recorded salinities, and a positive (non-significant) trend was observed between Mg/Ca and water temperature. Further assessment of environmental and biological controls on element incorporation are required; however, Ba/Ca in D. deltoides shells appears a suitable palaeo-salinity tool and has the potential to provide an easily accessible and valuable proxy to gain insights into past environmental conditions over extensive time scales.